266 LOUIS PASTEUR. 



hamper it. In scientific discussions, it is not as in 

 politics,' he added with a smile, ' where demonstration 

 is often difficult. In the natural sciences, doctrines 

 must be based on an assemblage of results, of ob- 

 servations, and of experiments. If a doctrine is 

 challenged, it seldom happens that its truth or 

 falsehood cannot be established by the application 

 of some crucial test. Even a single experiment 

 will often suffice either to refute or consolidate the 

 doctrine.' 



Reviewing the labours of the past forty years, 

 Pasteur then called to mind the numerous controver- 

 sies in which he had been engaged. Not only had he 

 been attacked by Pouchet and Joly on the question of 

 spontaneous generation, by Liebig on the subject of 

 fermentation, by Germans and Italians regarding the 

 attenuation of virus, but every one of his assertions 

 had been met with such passionate opposition that, 

 from sheer weariness, he had invariably ended by 

 referring the matter to some authorised commission, 

 only asking it to put an end to all strife by coming to 

 some definite decision. 



The upshot was at times somewhat amusing. For 

 instance, when Pasteur described to the Academy of 

 Medicine how, simply by lowering the temperature of 

 a hen, he had made her susceptible to inoculation with 

 splenic fever, the facts were at once denied by M. 

 Colin, a professor of the school of Alfort. Pasteur 



